The present invention relates to drive axles, and particularly those arrangements on a vehicle wherein plural drive axles are arranged in tandem. Tandem drive axle arrangements are commonly employed in heavy over-the-road trucks and off-the-road vehicles requiring the additional traction of plural driving axles. Typically, in heavy over-the-road trucks, the axle adjacent the powertrain driveshaft is the forward one of the tandem axles. In such arrangements, the forward drive axle has an input shaft connected to the vehicle power train driveshaft, and the axle has an axially coincident output shaft adapted for connection to the second trailing drive axle.
Axle arrangements of the aforesaid type usually employ an inter-axle differential between the axle input and output shaft, for transmitting driveshaft torque to both axles.
The upstream or forward drive axle in a tandem drive axle arrangement typically has a drive gear journalled on the input shaft receiving power from a power splitting inter-axle differential, which meshes with a countershaft gear attached to the axle drive pinion shaft with the drive pinion thereon engaging the axle ring gear. Heretofore, the countershaft or drive pinion shaft has been journalled with plural bearings to provide precision positioning of a drive pinion on the ring gear to minimize movement of the drive pinion with respect to the ring gear during power transmission.
Typically in heavy truck and off-the-road drive axles, the drive pinion shaft is journalled in bearings provided in a removable platform or block, with the countershaft gear cantilevered from the journals on the drive pinion shaft. The drive pinion typically has a pilot portion extending therefrom which is journalled in a bearing mounted on the axle housing upon which the ring gear and axle shafts are journalled.
Where the pinion shaft is journalled in a manner such that the countershaft gear is cantilevered from journals or bearings, problems have been encountered in providing adequate rigidity of the pinion shaft and for maintaining the precision positioning of the countershaft gear drive pinion with respect to the drive gear ring gear during high torque operation. Likewise, where the pinion shaft is journalled in a manner such that the drive pinion is cantilevered from journals or bearings, problems have been encountered in providing adequate rigidity during high torque operation.
Where the countershaft or pinion shaft has been mounted with the countershaft gear having journals supporting the countershaft on both sides of the countershaft gear, it has been difficult to provide for assembly of the overall drive axle assembly because the end journal for the countershaft was mounted in the cover or carrier housing portion of the axle assembly. This required complete assembly of the entire axle assembly in order to position the pinion shaft with respect to the ring gear and resulted in a costly and cumbersome assembly of the axle in high volume production.
It has therefore been desirable to find a way or means of supporting a drive axle countershaft for the drive pinion in a manner which does not leave the countershaft gear cantilevered from the bearings and which permits assembly of the countershaft and bearings into the axle housing for positioning the drive pinion with respect to a ring gear with a minimum number of bearings in a manner which permits ease of adjustment of the pinion position before the axle housing cover is installed.